1. Field of the Invention
The present invention generally relates to an interdigitated electrode structure, and more particularly to a new structure for a pair of electrodes using conductive polymers, and a method for producing the same.
2. Description of the Related Art
An interdigitated electrode structure is used in applications where it is desirable to form a large perimeter surface area for interaction between the electrodes. Applications using this type of structure may include capacitors, sensors, and detectors. In a conventional interdigitated structure, the proximity of the electrodes is limited by a minimum lithographic feature, and hence the capacitance, or electric field intensity between the electrodes is constrained by the lithographic process.
Electronically conducting polymers, particularly derivatives of polypyrrole and polyaniline, in which the conducting form of the polymers is soluble in appropriate organic solvents, have been used in many electronic applications. These polymers can be applied onto silicon wafers by spin-on or silk screening techniques. For example, conducting polypyrrole has been proposed as an ingredient to make passive elements such as resistors, capacitors and inductors in multichip modules or printed wiring boards, as disclosed in U.S. Pat. No. 5,855,755, the complete disclosure of which is incorporated by reference herein.
Moreover, polypyrrole and polythiophene derivatives have been used in solid state electrochromic devices. The polypyrrole conducting polymer can be made to be photosensitive by adding appropriate silver salts and photoinitator additives, as disclosed in U.S. Pat. No. 5,919,402, the complete disclosure of which is incorporated by reference herein. It has been discovered that under optimized conditions, the conductivity value for poly (3-methylthiophene) is 5.7 xcexa9xe2x88x921 cmxe2x88x921. Electrical conductivity can be further increased by incorporating metal particles such as nanoparticles of silver or copper in the polymer formulation. Thus, there is a need for an improved interdigitated electrode structure, which is capable of providing higher capacitance or electric field intensity between electrodes on electrical components of printed circuit boards and multichip modules, etc.
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional interdigitated electrode structure the present invention has been devised, and it is an object of the present invention to provide a structure and method for an improved interdigitated electrode structure. It is a further object of the present invention to increase the capacitive coupling between a pair of conductive electrodes on a substrate. The capacitive coupling will be a function of the distance between the pair of electrodes, and will increase as the electrodes are brought into close proximity.
Another object of the present invention is to provide a structure for a pair of electrodes which are self-aligned to each other. The self-aligned formation of the pair of electrodes means that the patterning manufacturing process will be insensitive to variations in the positional placement of the pattern on the substrate. Still another object of the present invention is to provide a method for forming the pair of electrodes using a single lithographic masking layer where the material modification of one of the electrodes causes an overhanging region to be formed on a first electrode which is used in the formation of the second electrode.
Yet another object of the present invention is to provide a structure which consists of a pair of electrodes which are electrically isolated, yet closer in proximity than the minimum resolvable lithographic feature size of the imaging system used to pattern the electrodes. The proximity of the electrodes is determined by the chemical surface modification, and the physical deposition of the second electrode, and not by the lithographic resolution as is the case in a conventional structure.
It is still another object of the present invention to provide a structure and method for the use of a conductive polymer for one or both electrode elements in a structure where the offset between the pair of electrodes is provided by a chemical surface modification (xe2x80x9cswellingxe2x80x9d) of the first electrode, and an anisotropic deposition of the second electrode which is shadowed by the first electrode.
In order to attain the objects suggested above, there is provided, according to one aspect of the invention a method of producing an electrode device, which comprises the steps of first depositing a conductive polymer material on a substrate. Then, patterning a mask on top of the conductive polymer. Third, forming spaced regions on top of the substrate. Next, the mask is removed from the conductive polymer. After which, the conductive polymer is expanded such that an upper part of the conductive polymer upwardly slopes from the lower part of the conductive polymer material. Then, a second conductive material is deposited on top of the first conductive polymer material, and in the spaced regions, which are located on the substrate. Finally, several electrical connections are placed on the device.
The benefits of this invention are several. For example, the present invention provides for a self-aligned pair of electrodes, which can be easily fabricated. Furthermore, the present invention provides for a single lithographic masking level, and for sub-lithographic features. Additionally, the structure of the present invention provides for the sub-lithographic proximity of the upper and lower electrodes.